An illumination optical system that uses a rod integrator to obtain uniform illumination light is a known illumination optical system for a projector.
Patent Document 1 describes a DLP (Digital Light Processing) projector provided with this type of illumination optical system.
The above-described DLP projector includes first to third laser array light sources having substantially identical angles of divergence, an illumination optical system, a Total Internal Reflection (TIR) prism, a display element composed of a Digital Micromirror Device (DMD), and a projection lens.
Here, the angle of divergence is an angle that is twice the angle formed by the outermost light ray and the center light ray (half-angle of divergence) when divergent luminous flux is viewed from a direction perpendicular to the plane that contains the center light ray of the divergent luminous flux.
The first laser array light source emits red laser light, the second laser array light source emits green laser light, and the third laser array light source emits blue laser light.
The illumination optical system includes first to third reflecting mirrors, first and second dichroic mirrors, a concave lens, a rod integrator, and a relay optical system.
The rod integrator is composed of, for example, a glass body in the shape of a quadrangular prism. One of the two end surfaces of the rod integrator is the incident surface, and the other is the exit surface.
In the rod integrator, luminous flux that entered the incident surface is propagated within the rod while being repeatedly reflected by the inner surfaces of the rod and then exits from the exit surface. The multiple reflections in the process of being propagated within the rod make the luminance of the incident luminous flux uniform. At the exit surface of the rod, a plurality of two-dimensional light source images are produced in matrix form depending on the number of reflections.
A concave lens, first dichroic mirror, second dichroic mirror, and first reflecting mirror are arranged in that order from the exit surface of the rod integrator.
The first reflecting mirror reflects the blue laser light from the third laser array light source toward the second dichroic mirror. The second dichroic mirror reflects the green laser light from the second laser array light source toward the second dichroic mirror.
The second dichroic mirror has spectral reflection properties that enable transmission of light of the blue wavelength band and reflection of light of the green wavelength band. Blue laser light from the first reflecting mirror is transmitted by the second dichroic mirror and irradiated into the first dichroic mirror. Green laser light from the second reflecting mirror is reflected by the second dichroic mirror, and this reflected light is irradiated into the first dichroic mirror on the same optical path as the blue laser light.
The third reflecting mirror reflects the red laser light from the first laser array light source toward the first dichroic mirror.
The second dichroic mirror has spectral reflection properties that enable transmission of light of the blue wavelength band and light of the green wavelength band and reflection of light of the red wavelength band. The blue laser light and green laser light from the second dichroic mirror are transmitted though the first dichroic mirror and irradiated into the concave lens. The red laser light from the third reflecting mirror is reflected by the first dichroic mirror, and this reflected light is irradiated into the concave lens on the same optical path as that of the blue and green laser light.
The concave lens acts to disperse the red, green, and blue laser light from the first dichroic mirror. The red, green, and blue laser light from the concave lens is entered into the rod integrator from the incident surface of the rod.
The relay optical system is arranged on the exit surface side of the rod integrator. The relay optical system acts to form an image of the light source image that was formed on the exit surface of the rod integrator on the effective display region of the display element.
The TIR prism is provided between the relay optical system and the display element. The luminous flux from the relay optical system is irradiated into the display element by way of the TIR prism. The display element spatially modulates the luminous flux to form image light. The image light that is formed by the display element is irradiated into the projection lens by way of the TIR prism.
In the above-described illumination optical system, the optical path lengths of the laser light of each color from each laser array light source to the incident surface of the rod integrator are the same, and the angles of divergence of each laser array light source are also the same. As a result, the laser light of each color that is emitted from each laser array light source is entered into the rod integrator with the same angle of divergence, is propagated within the rod, and is then exited from the rod integrator with the same angle of divergence.
Because the angle of divergence of the laser light of each color that is exited from the rod integrator is the same, the irradiation ranges of the laser light of each color that is irradiated on the display element by way of the relay optical system also coincide. As a result, the irradiation range of the laser light of each color can be caused to coincide with the effective display region on the display element by appropriately setting the magnification of the relay optical system.
Recent projectors include projectors in which laser light is supplied from an external light source device to the illumination optical system by way of optical fiber.
An external light source is provided with a red laser light source, a green laser light source, and a blue laser light source. The green laser light and blue laser light are supplied to the illumination optical system by a first optical fiber. The red laser light is supplied to the illumination optical system by a second optical fiber.
The angles of divergence of each of the green laser light and blue laser light that are emitted from the first optical fiber are substantially identical. The angle of divergence of red laser light emitted from the second optical fiber differs from the angle of divergence of the green laser light and blue laser light.
When the above-described external light source device is applied to the DLP projector described in Patent Document 1, the illumination optical system is configured such that green and blue laser light that is emitted from a first optical fiber is entered into one of the surfaces of a second dichroic mirror, and red laser light emitted from a second optical fiber is entered into the other surface of the second dichroic mirror.
The red laser light and the green and blue laser light are synthesized by the second dichroic mirror and then irradiated into the rod integrator by way of the concave lens.